Focused acoustic waves (or shockwaves, the terms being used interchangeably throughout) are being used increasingly in medical applications. For example, acoustic waves are used for tissue ablation, diagnostic imaging, drug delivery, breaking up concretions in the body such as kidney stones, treating orthopedic diseases, combating soft tissue complaints and pain, and other therapies which employ heat, cavitation, shock waves, and other thermal and/or mechanical effects for therapeutic purposes.
The prior art typically converts electrical energy into acoustic waves, such as by generating a strong pulse of an electric or magnetic field, usually by capacitor discharge, converting the electromagnetic field into acoustic energy, and directing the energy to a target by means of an associated focusing apparatus.
Point sources for the generation of acoustic waves in a lithotripter are described in various patents, such as U.S. Pat. No. 3,942,531 to Hoff et al., and U.S. Pat. No. 4,539,989 to Forsemann et al. A planar source for generation of acoustic waves is described, for example, in U.S. Pat. No. 4,674,505 to Pauli et al.
Cylindrical sources for generation of acoustic waves are described, for example, in U.S. Pat. No. 5,058,569 to Hassler et al., and U.S. Pat. No. 5,174,280 to Gruenwald et al. Spherical sources are also mentioned in the background of U.S. Pat. No. 5,174,280.
A truncated conical acoustic wave source is described in U.S. Pat. No. 6,869,407 to Ein-Gal, the disclosure of which is incorporated herein by reference. The background section of U.S. Pat. No. 6,869,407 includes a brief description of the manner by which acoustic waves are produced by point, spherical, planar, and cylindrical sources and a description of the limitations of each of these prior art acoustic wave generation apparatuses.